2Checking Available Versions

Checks the currently available version on the PLT website
(http://download.plt-scheme.org) and returns a value that
indicates the current state of the curent installation:

`ok – You’re fine.

`(ok-but,version) – You have a fine stable
version, but note that there is a newer alpha version available
numbered version.

`(newer,version) – You have an old
version. Please upgrade to version.

`(newer,version,alpha) – You have an
old-but-stable version, please upgrade to version; you
may consider also the newer alpha version numbered
alpha.

`(error,message) – An error occurred, and
message is a string that indicates the error.

`(error,message,additional-info) – An error
occurred; message is a string that indicates the
error, and additional-info is a string containing a
system error. The additional-info content is always
parenthesizes, so message is a short error and
(string-appendmessage" "additional-info) is a
verbose one.

Converts the version string into an integer. For version
"X.YY.ZZZ.WWW", the result will be XYYZZZWWW.
This function works also for legacy PLT Scheme versions, by
translating "XYY.ZZZ" to XYYZZZ000. The
resulting integer can thefore be used to conveniently compare any two
(valid) version strings. If the version string is invalid the
resulting value is #f.

Note that this is the only function that deals with legacy version
strings.